Hello,
I bought a home back in 2019 for $305,000. (i refinance the $305k home in 2020 into an IRRRL).. which means I dont have to live in the property.
-My downpayment was $0
-The VA Loan Limit in New Jersey is: $822,375
-My COE is: Basic Entitle is $36,000. My COE also states: Additional entitlement is available for most loans in excess of $144,000. In such cases, the entitlement amount is 25% of the VA lon limit for the county where the property is located.
Im not too sure how much entitlement i used already. I want to buy a second home for $280k with my VA loan with a $0 downpayment.
Is this still doable? If not, how much can I afford to put on a home with $0 dowpayment, while keeping my first home that was refinanced into an IRRRL?
thank you! 
Not always, but usually the amount entitlement a VA loan uses up is 25% of the original loan amount, so if the original loan was $305,000 then there is a good chance you've used up $76,250 in entitlement.
Your current Certificate of Eligibility will say how much entitlement your existing VA loan is using up. Have you obtained a new one? For example it may look like the below:
Assuming you have used up $76,250 in entitlement that means you'll need to deduct that from 25% of the county loan limit to determine your remaining entitlement. If the county you are buying in has a county loan limit of $822,375 then 25% of that is $205,593 minus $76,250 of used entitlement = $129,343 in remaining entitlement. Multiply that by 4 and that is the max sales price you'd be eligible for 100% financing on, which comes out to $517,372.
If you haven't used up any entitlement then VA doesn't have a limit on what you'd be eligible to finance without a down payment, it'd just come down to how much you could qualify for and if there is a lender out there that would do that high of a loan amount (most cap out at $1,500,000 to $3,000,000).